Horizontal deflection circuits as may be used in television and higher speed cathode ray tube (CRT) display devices typically employ high frequency sweep rates, which are most efficiently provided when the deflection or flyback circuit is operated to provide a resonant retrace mode. Accordingly, the deflection coil or flyback inductor is resonated with a selected capacitor to form a circuit wherein the voltage across the deflection or flyback inductor during the retrace interval is a half sine voltage waveform. At the end of the retrace interval, a flyback deflection clamping diode is used to inhibit the voltage polarity reversal, thus causing a flow of current through the inductor to provide the initial portion of the linear deflection. However, the flyback clamping diode typically exhibits a finite turn-on time which causes a delay in the inhibition of the opposite polarity voltage across the deflection coil until the diode becomes fully conductive. The duration required to cause the clamping diode to conduct is typically long enough to cause significant voltage to develop across the diode and short enough to provide a high energy pulse having high frequency components. As the diode begins to conduct, energy of the diode generated voltage pulse is dissipated throughout the deflection circuit. However, the deflection coil typically exhibits a self resonance 10 to 20 time the sweep period, and becomes shock excited by the flyback clamp diode produced pulse. The result of this shock excited self resonance appears as intensity variations in the displayed image. When the circuit is used for horizontal deflection, this intensity variation appears as vertically extending regions or bands of alternating enhanced and reduced intensity for several cycles at the edge of the CRT screen.
Heretofor the suppression of the unwanted high voltage pulse has been addressed by attempting to manufacture a diode having a reduced turn-on time for this application. However, the improvement provided by decreasing turn on times is negated by the trend to increase deflection rates, and the problem persists.